In the medical field, multi-gradation monochrome images are generated by medical image generation apparatuses such as computed tomography (CT) systems, magnet resonance imaging (MRI) systems, computed radiography (CR) systems, flat panel detectors (FPD), and ultrasonic diagnostic apparatuses and used for diagnoses and other purposes.
At the time of utilizing a multi-gradation monochrome image, the multi-gradation monochrome image is displayed in a display apparatus such as, for example, a cathode ray tube (CRT), or the displayed multi-gradation monochrome image is printed on paper by an output apparatus such as a printer.
It is important to maintain gradation reproducibility in the display apparatus and the output apparatus, so that the multi-gradation image can be utilized for its intended purpose.
Since, in an output apparatus such as, for example, a printer, characteristics of each unit are easy to subtlety change, maintenance of gradation reproducibility is typically performed by calibration.
However, when the characteristic of each unit in the output apparatus greatly changes, it becomes difficult to maintain the gradation reproducibility using the calibration, and a reproducible gradation range (the number of gradations) is reduced in some cases. In this case, since it is difficult to accurately reproduce gradations outside the reduced gradation range on the paper, it may become difficult to detect a tumor or the like that was detectable before that.
One known technique involves increasing a gradient in a portion of an optical density area. In this case, the balance of an entire image is deteriorated, and a situation in which the gradation reproducibility is reduced may occur.
In particular, in a medical image system, there is the necessity of focusing on and observing in detail an image range within a medical image, suspected of being a tumor or the like. However, in the past, in such a case, there has been a limit on securing the gradation reproducibility of an image within a focused image range while achieving the gradation balance of the entire image.